[OpenAFS] openafs on Fedora 12?

Rainer Toebbicke rtb@pclella.cern.ch
Thu, 10 Dec 2009 09:37:24 +0100

Chas Williams (CONTRACTOR) wrote:

> i still wonder if the cache manager shouldnt open a single file (sparse
> mode) and just seek/read/write.  this would solve a couple of potential
> problems with other filesystems as well.

There are some issues with the canonical approach of just using one file and 
seek to chunkno*chunksize:

1. directories are read in total, regardless of chunk boundaries;

2. it is, to my knowledge and on a POSIX level, not possible to "free" parts 
of a file. Hence, if the number of chunks in the cache exceeds the size of 
/usr/vice/cache you run out of space;

3. unless done carefully, if you re-write parts of a file the system may end 
up reading it in first (partial blocks).

With individual cache files and well-placed truncate() calls these issues go 

I guess none of those are unsolvable, having just a single file (or set of 
files on different discs) could make life easier and speed up things by 
eliminating double buffering (afs's VM cache + cache chunks's VM cache).

Rainer Toebbicke
European Laboratory for Particle Physics(CERN) - Geneva, Switzerland
Phone: +41 22 767 8985       Fax: +41 22 767 7155